Refrac liner with isolation collar

ABSTRACT

A collar for a refracturing liner includes a body having a first end and a second end, the first end being configured to connect to a first liner segment, and the second end being configured to connect to a second liner segment. The body defines an inner diameter surface extending between the first and second ends. The collar also includes at least one radial expansion feature formed in the body, wherein the at least one radial expansion feature is configured to deform radially outward when the body is axially compressed, and wherein the at least one radial expansion feature is configured to engage a surrounding tubular and form a fluid flow barrier therewith.

BACKGROUND

Hydraulic fracturing is a treatment process used in the oilfield to create preferential flowpaths (cracks) in rock formations, such as shale, that are otherwise resistant to allowing fluid flow therethrough. This process often proceeds in a cased well. Thus, the cemented-in, steel casing is first perforated, e.g., using a perforation gun. Next, fracturing fluid is pumped into the well and directed through the perforations, and outward, into the formation. The high pressure of the fluid causes cracks to propagate in the formation, and proppant can be used to prevent the cracks from closing. Fluids, such as hydrocarbons, are thus allowed to flow more freely through the formation via the cracks.

However, shales or other tight formations, e.g., in a horizontal well section, may decline in production so an economic limit of the well is reached sooner than desired. One technique to continue producing such a well is to fracture the formation again (“refrac”) and thereby create new fractures in the formation. This may be accomplished by squeezing off the old fracture with cement, re-perforating the well between the old fractures, and then re-fracturing the well through the new perforations.

Because of uncertainties associated with cement squeezing, some wells are refractured by setting patches in the casing to cover the old perforations. After the casing patches are set, new perforations are sequentially created between the casing patches, and the new perforations are sequentially traced. In order to isolate a zone that has been fracked from the next zone to be fracked in such a well, a bridge plug or similar tool is passed through the casing and casing patches to a location above where the new perforations have been formed, and then set against the casing, allowing pressure to be delivered to the next set of perforations. However, setting individual patches can be time consuming and may again have problems with uncertainty, e.g., in locating all the prior casing perforations, ensuring proper expansion, etc.

Accordingly, liners have recently been used in place of such patches. The liners are made up of a string of tubulars that fit inside the casing, and can be run into place in the casing. The liners may then be hung in the casing, resulting in a “microannulus” between the liner and the casing. The liner may then be expanded so as to obstruct the perforations; however, expandable liners are occasionally unreliable. Accordingly, it may be desired to otherwise fill the microannulus, e.g., with cement; however, it may be difficult to circulate cement through the microannulus, due to the small flowpath area.

SUMMARY

Embodiments of the disclosure may provide a collar for a refracturing liner includes a body having a first end and a second end, the first end being configured to connect to a first liner segment, and the second end being configured to connect to a second liner segment. The body defines an inner diameter surface extending between the first and second ends. The collar also includes at least one radial expansion feature formed in the body, wherein the at least one radial expansion feature is configured to deform radially outward when the body is axially compressed, and wherein the at least one radial expansion feature is configured to engage a surrounding tubular and form a fluid flow barrier therewith.

Embodiments of the disclosure may also provide a method for refracturing a well. The method includes positioning a liner within a perforated casing of a well that extends through a formation, such that an annulus is formed between the liner and the perforated casing. The liner includes a plurality of liner segments connected together by a plurality of isolation collars. The method further includes axially compressing the liner. Axially compressing the liner causes at least some of the plurality of isolation collars to deform radially outwards and at least partially block fluid flow in the annulus. The method also includes perforating the liner so as to create new perforations axially between two of the plurality of isolation collars, and pumping fracturing fluid into the formation through the new perforations.

Embodiments of the disclosure may further provide a refracturing system that includes a first liner segment, a second liner segment, and an isolation collar connecting together the first and second liner segments. The isolation collar is configured to be deformed radially outward by pressing the first and second liner segments together, so as to form at least a partial barrier to fluid flow through an annulus formed between the first and second liner segments and a surrounding tubular.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:

FIG. 1 illustrates a side, schematic view of a refrac system deployed in a well, according to an embodiment.

FIG. 2 illustrates a side, cross-sectional view of a collar of the refrac system, with the collar in a run-in configuration, according to an embodiment.

FIG. 3 illustrates a side, cross-sectional view of the collar in a set configuration, according to an embodiment.

FIG. 4 illustrates a side, cross-sectional view of the refrac system in the well with the collars being actuated into the set configuration using a workstring, according to an embodiment.

FIG. 5 illustrates a side, cross-sectional view of the refrac system in the well with the collars being actuated into the set configuration using a packer, according to an embodiment.

FIG. 6 illustrates a side, cross-sectional view of the refrac system in the well with new perforations formed therein, according to an embodiment.

FIG. 7 illustrates a flowchart of a method for refracturing a well, according to an embodiment.

DETAILED DESCRIPTION

The following disclosure describes several embodiments for implementing different features, structures, or functions of the invention. Embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference characters (e.g., numerals) and/or letters in the various embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed in the Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the embodiments presented below may be combined in any combination of ways, e.g., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure.

Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Additionally, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. In addition, unless otherwise provided herein, “or” statements are intended to be non-exclusive; for example, the statement “A or B” should be considered to mean “A, B, or both A and B.”

FIG. 1 illustrates a side, schematic view of a re-fracturing (or “refrac”) system 100 deployed in a wellbore 102 formed in a subterranean formation 103, according to an embodiment. In this embodiment, the refrac system 100 includes a liner assembly 104, which is positioned in a casing 106 that is cemented in place in the wellbore 102. The casing 106 may have been previously perforated, thus defining perforations 107, as part of an earlier hydraulic fracturing operation. The earlier hydraulic fracturing operation may have caused the illustrated fractures 108 to form in the formation 103 through the perforations 107. As mentioned above, in some cases, it may be desirable to again fracture (“re-fracture”) the formation 103, so as to form new fractures and/or expand the existing fractures 108. To do so, the perforations formed in the casing 106 by the previous operations may be substantially blocked from communication with one another using the refrac system 100 disclosed below.

The liner assembly 104 generally includes two or more liner segments 110, 112, which are connected together, end-to-end, via collars 111. In some embodiments, many such liner segments 110, 112 may be joined together, with at least some of the segments joined together by the collars 111. The liner segments 110, 112 may be expandable tubulars, and/or may be made from any suitable type of material, such as steel. The liner assembly 104 is positioned within the casing 106 such that an annulus 114 is defined radially therebetween. It will be appreciated that the liner assembly 104 may not be positioned entirely concentric the casing 106, and thus the radial dimension of the annulus 114 may vary as proceeding around the annulus 114. The annulus 114 may be relatively small in comparison to an annulus 116 formed between the casing 106 and an uncased wall 118 of the wellbore 102, and thus the annulus 114 may be referred to as a “microannulus” 114. The prefix “micro” in “microannulus” is not meant to connote any particular scale size, however, but merely refers to the annulus 114 being smaller than the annulus 116.

The liner assembly 104 may also include an anchor 115 that is coupled to the liner segments 110, 112 and the casing 106. The anchor 115 may be any suitable type of liner hanger that engages the casing 106 and allows the liner segments 110, 112 to be held in place with respect thereto. In some embodiments, the anchor 115 may be positioned uphole of the uphole-most perforation 107 in the casing 106, such that the liner assembly 104 extends across all of the perforations 107 in the casing 106.

At least some of the collars 111 may be isolation collars. The isolation collars 111 may be configured to deform radially outward, so as to span the annulus 114 and provide a flow barrier therein. As such, the deformed isolation collars 111 may prevent communication between the perforations 107 via axial flow in the annulus 114. The isolation collars 111 may be deformed radially outward by pressing adjacent liner segments 110, 112 toward one another. Such axial compressive forces may be generated in a variety of ways, examples of which are discussed below.

FIG. 2 illustrates a simplified, side, cross-sectional view of the adjacent liner segments 110, 112 and the isolation collar 111 therebetween, according to an embodiment. In particular, FIG. 2 illustrates the isolation collar 111 in a run-in configuration.

The isolation collar 111 may have a body 200 with first and second ends 202, 204 at the opposite axial extents thereof. The first end 202 may be coupled to the liner segment 110 and the second end 204 may be coupled to the liner segment 112. Both connections may be threaded, e.g., the liner segments 110, 112 may provide pin-end connections that are threaded into engagement with box-end connections of the collar 111, although any configuration of threaded or otherwise made-up connections may be employed.

The body 200 may be generally cylindrical and hollow, defining an inner diameter surface 210 therethrough that extends entirely between the first and second ends 202, 204, so as to provide fluid communication between the liner segments 110, 112. The isolation collar 111 may also define an outer diameter surface 212 extending entirely between the first and second ends 202, 204. In some embodiments, the outer diameter surface 212 may have the same or substantially the same radius as the outer radial dimension of the liner segments 110, 112, but in other embodiments, may be smaller or larger.

The isolation collar 111 may include at least one radial expansion feature 220. The at least one radial expansion feature 220 may be a part of the isolation collar 111 that is configured to be deformed radially outward, such that the outer diameter of the isolation collar 111 (e.g., part of the body 200) is increased at the at least one radial expansion feature 220 more than the outer diameter of the body 200 away from (i.e., not at) the at least one radial expansion feature 220. In an embodiment, the at least one radial expansion feature 220 may be configured to engage a surrounding tubular (e.g., the casing 106 of FIG. 1) so as to form a barrier to fluid flow axially along the outer diameter surface 212 of the collar 111. Such a barrier may be a complete seal, a partial seal, or an impediment to fluid flow that reduces fluid communication but does not prevent it. In some embodiments, the at least one radial expansion feature 220 may include an elastomeric seal, a grit (e.g., WEARSOX®), and/or another component configured to provide a complete seal, increase anchoring force, resist abrasion of the collar 111, etc.

In an embodiment, the at least one radial expansion feature 220 may be a recess 240 formed in the inner diameter surface 210. For example, the recess 240 may extend outward into the body 200, toward the outer diameter surface 212, such that the radial thickness of the body 200 is decreased. In a specific embodiment, the cross-section of the recess 240 may be arcuate, but other cross-sectional shapes may be used.

As shown, in some embodiments, the at least one radial expansion feature 220 may also include a second recess 242. The second recess 242 may be spaced axially apart from the recess 240, and may be formed substantially the same as the recess 240. In other embodiments, the at least one radial expansion feature 220 may include any number of recesses 242.

FIG. 3 illustrates a simplified, side, cross-sectional view of the liner segments 110, 112 and the isolation collar 111, with the isolation collar 111 in a deformed or set configuration, according to an embodiment. As shown, in this configuration, the body 200 at the recesses 240, 242 (i.e., the radial expansion feature 220) has increased in radial dimension by deforming (bending) radially outwards. That is, in some embodiments, the outer diameter surface 212 may be radially larger at the at least one radial expansion feature 220 as compared to the outer diameter surface 212 away from the at least one radial expansion feature, when the isolation collar 111 is in the deformed configuration.

The recesses 240, 242 may have an axial width that is sufficient to allow axial compression and radial enlargement thereof such that the body 200 on the radial outside of the recesses 240, 242 is able to engage the surrounding tubular (e.g., casing 106) without fracturing. Accordingly, in moving from the run-in configuration to the deformed configuration, the axial length of the isolation collar 111 may decrease, while the radial dimension of the body 200 at the at least one radial expansion feature 220 may increase. By contrast, areas of the body 200 away from (e.g., not at or immediately adjacent to) the at least one radial expansion feature 220 may not be deformed radially outward by the axial compression, or may be deformed radially outward to a lesser degree (e.g., by thermal expansion, or to a relatively small degree as the at least one radial expansion feature 220 is expanded).

FIG. 4 illustrates a schematic, cross-sectional view of the refrac system 100 deployed in the wellbore 102 and ready to be set, according to an embodiment. In this view, a work string 400 of the refrac system 100 has been deployed through the liner assembly 104. The work string 400 may be configured to apply a compressive force on the liner assembly 104. In particular, the work string 400 may have a swage or another tool configured to allow the work string 400 to pull in an uphole direction on the liner assembly 104. Pulling the liner assembly 104 using the work string 400 may result in the adjacent liner segments 110, 112 being forced together, e.g., as each subjacent liner segment 112 pushes uphole toward the superposed liner segment 110. As such, the isolation coupling 111 may be axially compressed therebetween, causing the radial expansion feature(s) 220 of the isolation coupling 111 to deform radially outwards and span the microannulus 114, thereby preventing communication between axially separate perforations 107.

FIG. 5 illustrates a schematic, cross-sectional view of the refrac system 100, again deployed in the wellbore 102 and ready to be set, according to an embodiment. In this embodiment, the refrac system 100 additionally includes a packer or another obstruction 500 that is deployed into the wellbore 102 and landed on the uphole side of the liner assembly 104. A pressure may then be applied, e.g., by pumping fluid into the wellbore 102, to the packer 500. The packer 500 may prevent the fluid from flowing into the liner assembly 104 and/or into the microannulus 114, but may not be anchored into the casing 106. As such, the pressure on the packer 500 may be applied as a downhole directed force on the liner assembly 104. This downhole directed force may axially compress the isolation collars 111, resulting in the isolation collars 111 deforming radially outward, as discussed above, and thereby setting the refrac system 100 in the casing 106. Thereafter, the packer 500 may be retrieved or otherwise removed (e.g., dissolved, milled, etc.), or may include a bore therethrough that is openable.

In other embodiments, the obstruction 500 may be a seal that is landed and retained at the uphole side of the liner assembly 104. A packer may be set in the toe of the wellbore 102 as well, e.g., proximal to the downhole end of the liner assembly 104. The liner assembly 104 may be free floating in the wellbore 102, and thus increasing pressure in the wellbore 102 may result in the entire liner assembly 104 being forced downhole, into engagement with the toe of the wellbore 102, thereby axially compressing the liner assembly 104, including the isolation collars 111. The seal/obstruction 500 may then be removed to commence fracturing operations.

FIG. 6 illustrates a schematic, cross-sectional view of the refrac system 100 after having been set, according to an embodiment. As such, the isolation collars 111 are set (e.g., deformed or energized), and prevent or at least reduce fluid communication between axially offset fractures 108. As such, plug-and-perf operations may commence within the liner assembly 104, in the liner segments 110, 112 between the isolation collars 111. In particular, plugs 600 may be deployed into the liner assembly 104 and set, the liner assembly 104 may be perforated above the plug 600, thereby creating new perforations 602 in the liner assembly 104, which may either communicate with the old perforations 107 in the casing 106 or form new perforations in the casing 106. Fracturing fluid may be pumped down to the plug 600 and radially outward through the new perforations 602 in the liner assembly 104. The high-pressure fluid may then flow outward through the casing 106 and the annulus 116 and into the formation 103, while being impeded from travel through the microannulus 114. This process may then be repeated for another set of perforations at a location uphole of the prior location.

FIG. 7 illustrates a flowchart of a method 700 for refracturing a well, according to an embodiment. The method 700 may proceed using an embodiment of the refrac system 100 discussed above and is thus described with reference thereto. In other embodiments, the method 700 may use other systems or structures.

The method 700 may begin by positioning a liner assembly 104 within a perforated casing 106 of a wellbore 102, as at 702. As such, an annulus 114 is formed between the liner assembly 104 and the perforated casing 106. The liner assembly 104 includes a plurality of liner segments 110, 112, which may be connected together by a plurality of isolation collars 111.

In an embodiment, positioning the liner assembly 104 at 702 may include positioning the plurality of isolation collars 111 axially between existing perforations 107 in the perforated casing 106, such that the existing perforations 107 are covered by at least some of the plurality of liner segments 110, 112. Further, positioning the liner assembly 104 at 702 may, in some embodiments, include anchoring an uphole end of the liner above an uphole-most perforation 107 formed in the perforated casing 106.

The method 700 may also include axially compressing the liner assembly 104, as at 704. Axially compressing the liner assembly may cause at least some of the plurality of isolation collars 111 to deform radially outward and at least partially block fluid flow in the annulus, as indicated at 706.

In an embodiment, axially compressing the liner assembly 104 may proceed by positioning a work string inside the liner assembly, and pulling the work string uphole in the liner assembly 104. This may result in an uphole-directed force on the liner assembly 104, which compresses the liner segments 110, 112 and thus the collars 111 therebetween.

In another embodiment, axially compressing the liner assembly 104 at 704 includes placing a packer 500 (or another obstructing member) on an uphole and/or downhole end of the liner assembly 104 and increasing a pressure on the uphole end of the liner assembly 104, such that a force in the downhole direction is applied to the liner assembly 104, which axially compresses the liner assembly 104 and deforms the isolation collars 111 radially outwards.

Further, the method 700 may include perforating the liner assembly 104 so as to create new perforations axially between two of the plurality of isolation collars 111, as at 708. The method 700 may further include pumping fracturing fluid into the formation through the new perforations, as at 710.

In an embodiment, the method 700 may include positioning a plug 600 in the liner assembly 104 between two of the pluralities of isolation collars 111, as at 712. For example, the plug 600 may be positioned downhole of the new perforations. Further, the plug prevents the fracturing fluid from flowing axially through the liner assembly 104 and thereby directs the fracturing fluid radially outward into the formation through the new perforations.

As used herein, the terms “inner” and “outer”; “up” and “down”; “upper” and “lower”; “upward” and “downward”; “above” and “below”; “inward” and “outward”; “uphole” and “downhole”; and other like terms as used herein refer to relative positions to one another and are not intended to denote a particular direction or spatial orientation. The terms “couple,” “coupled,” “connect,” “connection,” “connected,” “in connection with,” and “connecting” refer to “in direct connection with” or “in connection with via one or more intermediate elements or members.”

The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A collar for a refracturing liner, comprising: a body having a first end and a second end, the first end being configured to connect to a first liner segment, and the second end being configured to connect to a second liner segment, wherein the body defines an inner diameter surface extending between the first and second ends; and at least one radial expansion feature formed in the body, wherein the at least one radial expansion feature is configured to deform radially outward when the body is axially compressed, and wherein the at least one radial expansion feature is configured to engage a surrounding tubular and form a fluid flow barrier therewith.
 2. The collar of claim 1, wherein the at least one radial expansion feature comprises a recess formed in the inner diameter surface of the body.
 3. The collar of claim 2, wherein the recess is arcuate in cross-section.
 4. The collar of claim 2, wherein the body has a reduced radial thickness where the recess is formed in comparison to a radial thickness of the body adjacent to the recess.
 5. The collar of claim 1, wherein the body is configured to deform radially outward at the at least one radial expansion feature to a greater extent the body deforms radially outward away from the at least one radial expansion feature.
 6. The collar of claim 1, wherein at the at least one radial expansion feature comprises a first recess formed in the inner diameter surface of the body and a second recess formed in the inner diameter surface of the body, the first and second recesses being spaced axially apart along the body.
 7. A method for refracturing a well, comprising: positioning a liner within a perforated casing of a well that extends through a formation, such that an annulus is formed between the liner and the perforated casing, wherein the liner comprises a plurality of liner segments connected together by a plurality of isolation collars; axially compressing the liner, wherein axially compressing the liner causes at least some of the plurality of isolation collars to deform radially outwards and at least partially block fluid flow in the annulus; perforating the liner so as to create new perforations axially between two of the plurality of isolation collars; and pumping fracturing fluid into the formation through the new perforations.
 8. The method of claim 7, wherein positioning the liner comprises positioning the plurality of isolation collars axially between existing perforations in the perforated casing, such that the existing perforations are covered by at least some of the plurality of liner segments.
 9. The method of claim 7, wherein positioning the liner comprises anchoring an uphole end of the liner above an uphole-most perforation formed in the perforated casing.
 10. The method of claim 7, wherein axially compressing the liner comprises: positioning a work string inside the liner; and pulling the work string uphole in the liner.
 11. The method of claim 7, wherein axially compressing the liner comprises increasing a pressure on an uphole end of the liner, such that the liner is pushed downhole.
 12. The method of claim 11, further comprising landing a packer on the uphole end of the liner, such that the pressure on the uphole end of the liner is applied to the liner via the packer.
 13. The method of claim 7, further comprising positioning a plug in the liner between two of the isolation collars, wherein the plug is positioned downhole of the new perforations, and wherein the plug prevents the fracturing fluid from flowing through the liner and thereby directs the fracturing fluid into the formation through the new perforations.
 14. A refracturing system, comprising: a first liner segment; a second liner segment; and an isolation collar connecting together the first and second liner segments, wherein the isolation collar is configured to be deformed radially outward by pressing the first and second liner segments together, so as to form at least a partial barrier to fluid flow through an annulus formed between the first and second liner segments and a surrounding tubular.
 15. The system of claim 14, wherein the surrounding tubular comprises a perforated casing.
 16. The system of claim 14, further comprising an anchor coupled to the first liner segment and configured to hang the refrac system from the surrounding tubular, wherein the isolation collar and the first and second liner segments are configured to receive a work string therethrough, such that the work string applies an uphole force on the second liner segment and presses the second liner segment towards the first liner segment, thereby pressing the first and second liner segments together and radially deforming the isolation collar.
 17. The system of claim 14, further comprising a packer engaging an uphole end of the first liner segment, wherein a pressure applied to the uphole end of the first liner segment causes the first liner segment to be pressed toward the second liner segment, thereby pressing the first and second liner segments together and radially deforming the isolation collar.
 18. The system of claim 14, wherein the isolation collar comprises: a body having a first end and a second end, the first and second ends being configured to connect to the first and second liner segments, respectively, wherein the body defines an inner diameter surface extending between the first and second ends; and at least one radially expansion feature formed in the body, wherein the at least one radial expansion feature is configured to deform radially outward when the body is axially compressed, wherein the body is configured to deform radially outward by a greater extent at the at least one radial expansion feature than the body deforms away from the at least one radial expansion feature, and wherein the at least one radial expansion feature is configured to engage the surrounding tubular and form the at least partial barrier.
 19. The system of claim 18, wherein the at least one radial expansion feature comprises a recess formed in the inner diameter surface of the body.
 20. The system of claim 18, wherein at the at least one radial expansion feature comprises a first recess formed in the inner diameter surface of the body and a second recess formed in the inner diameter surface of the body, the first and second recesses being spaced axially apart along the body. 